Blowable fuses have been used in a variety of applications to control the operative features of an integrated circuit. For example, such fuses have been used for the correction of bandgap references and data converters. Usually, this is done at the wafer probe stage and requires the use of substantial off-chip equipment.
In practice, such techniques have been found to be subject to certain limitations. One such limitation is that it is often desirable to operate upon the fuses not only at the wafer-probe stage, but also later, following packaging. Other limitations result from the amount of power which is required to operate (blow) such fuses. For example, the switching element provided on the integrated circuit for blowing the fuse must in practice occupy on the order of one-half of the total area of the blowable fuse circuit. Primarily, this is because the size of the switching element which is used to blow the fuse is responsive to the amount of current required to open the fuse, which continues to present a significant limitation. In addition, the amount of power required to blow the fuse has in practice been found to be potentially damaging to the passivation layer of the integrated circuit, which can permit the passage of moisture and the corrosion which can result from such moisture.
Efforts have been made to overcome these limitations. For example, De Wit et al., "A Low-Power 12-b Analog-to-Digital Converter with On-Chip Precision Trimming", IEEE Journal of Solid-State Circuits, Vol. 28, No. 4 (April, 1993), discloses the use of blowable fuses to reduce the capacitor ratio error in a data converter circuit. Circuits for accomplishing this are further described in U.S. Pat. Nos. 5,353,028 and 5,235,335. In an effort to allow programmable, on-chip adjustments to be performed after packaging, and at a lower voltage (power) level, De Wit et al. suggest the use of polysilicon fuses.
While such measures have offered some improvement upon the use of blowable fuses, still further improvement is considered necessary. In all cases, it remains important to ensure that such fuses are both safely and reliably blown. Moreover, the need for further reduction in the area occupied by such circuitry continues to be driven by the desire to provide a given integrated circuit with a greater number of fuses.